1. Field of the Invention
This invention relates to auxiliaries for formulating aqueous thickeners, more particularly based on polyurethanes, in liquid form and to aqueous thickener formulations produced with these auxiliaries. The invention also relates to the use of the thickener formulations in systems to be thickened, for example in water-based emulsion paints.
2. Discussion of Related Art
Polyurethane-based thickeners, of which the thickening properties can be described by an associative action mechanism, are suitable as auxiliaries for establishing Theological properties in water-based systems such as, for example, automotive and industrial lacquers, plasters and paints, printing inks and textile dyes, pigment printing pastes, pharmaceutical and cosmetic formulations, plant protection formulations and filler dispersions. The action mechanism of such thickeners is described, for example, in Polymers Paint Colour Journal, 181, 270 (1991). Besides polyurethanes, ethoxylated fatty alcohols additionally reacted in blocks or statistically with a small percentage of long-chain epoxides or nonionic polyacrylates or polyacrylamides partly esterified with long-chain fatty alcohols or even cellulose derivatives etherified with long alkyl chains may be used as associative thickeners in water-based systems. They are increasingly replacing or complementing the cellulose ethers traditionally used as thickeners in paints and lacquers and the traditional alkali-soluble polyacrylates. Associative thickeners have a number of advantages over conventional thickener systems including, for example,
a lower viscosity during incorporation, PA1 a lower tendency to splash during application, PA1 better color, PA1 higher gloss through less flocculation, PA1 lower sensitivity of the coatings to water, PA1 less vulnerability to microbial infestation, PA1 minimal reduction in the viscosity of the thickened dispersions on exposure to shearing (approaching newtonian flow behavior). PA1 R.sup.1 is an aliphatic hydrocarbon radical containing 6 to 10 carbon atoms and, more particularly, 8 carbon atoms, PA1 R.sup.2 represents alkylene radicals containing 2 to 4 carbon atoms and PA1 n is an integer of 3 to 7. PA1 R.sup.1 is an aliphatic hydrocarbon radical containing 6 to 10 carbon atoms and, more particularly, 8 carbon atoms, PA1 R.sup.2 represents alkylene radicals containing 2 to 4 carbon atoms and PA1 n is an integer of 3 to 7, as viscosity reducers in aqueous thickener formulations.
The production and use of such thickeners is described, for example, in U.S. Pat. No. 4,079,028 and in U.S. Pat. No. 4,426,485.
Although polyurethane-based thickeners have a far lower viscosity than polyacrylates or cellulose ethers for the same thickening effect, the formulation of polyurethane-based liquid thickeners still involves difficulties. In the form of aqueous solutions, known polyurethane thickeners have a very high viscosity which makes them very difficult to incorporate in aqueous systems.
Various attempts have been made in the past to reduce the viscosity of polyurethane thickeners. For example, their molecular weight has been reduced although this resulted in a seriously diminished thickening effect.
A standard method for reducing the viscosity of aqueous polyurethane thickener solutions is to add water-soluble low molecular weight solvents such as, for example, water-soluble monohydric or polyhydric alcohols. Serious disadvantages of this method are the deterioration in the performance properties, for example spreadability or stability, and the increased emission of volatile solvents.
The above-mentioned disadvantages of using low molecular weight solvents in thickener formulations can be overcome, for example, by supplying and processing the thickener in solid form. However, the disadvantages of formulating the thickener in solid form lie in additional process steps both during the production and subsequent processing of the thickener. In the first case, the thickener has to be isolated from the reaction medium and converted into powder form whereas, in the second case, the powder first has to be converted into a processable form by dissolution or swelling before or during its intended use so that final application is possible.
The possibility of reducing the viscosity of thickener systems by adding relatively large quantities of water appears uneconomical because it would involve an unwanted production in the concentration of active substance and, hence, an increase in the quantity applied.
Now, according to DE-A-43 10 702, alkoxylated alcohols or phenols may be added to reduce the viscosity of aqueous solutions of polyurethane thickeners, although they have to be used in high concentrations to achieve an adequate reduction in the viscosity of the thickener. The document in question also discloses the use of 2,4,7,9-tetramethyl-5-decine-4,7-diol in quantities of up to 25% by weight for reducing viscosity in aqueous thickener systems.
DE-A-36 30 319 describes the synthesis of polyurethane-based thickeners which themselves have a low viscosity. This document mentions the use of ethoxylated alcohols as "solubilizee". The adduct of 60 moles of ethylene oxide (EO) with 1 mole of tallow alcohol and the adduct of 12 moles of EO with nonylphenol are mentioned as examples of such solubilizers.
U.S. Pat. No. 4,636,326 discloses the use of mixtures of known polyurethane thickeners with dimer fatty acid esters in aqueous hydraulic fluids. The document in question mentions the use of nonionic surfactants as additive-dispersing auxiliaries. It does not refer to the use of ethoxylated fatty alcohols for reducing the viscosity of hydraulic fluids, nor does it mention such an effect.
Accordingly, the problem addressed by the present invention was to avoid the disadvantages mentioned in the foregoing and to provide a thickener formulation which would have a low viscosity and which would therefore be easy to handle. At the same time, however, the original properties of the thickener when used as intended in aqueous solution would remain largely intact.
It has now surprisingly been found that even an addition of about 10% by weight of adducts of 3 to 7 moles of EO and/or propylene oxide (PO) with short-chain fatty or Guerbet alcohols generally reduces the viscosity of aqueous thickener formulations to such an extent that the aqueous thickener formulations are convenient to handle.